The invention relates to rear projection screens and light filters, specifically those with a conformable coating over transparent microspheres.
Rear projection screens transmit an image from the back of the screen to the viewer on the opposite side of the screen. The image is affected by the amount of light transmitted by the screen or filter or throughput. Generally, screens and filters have been limited by their construction to the amount of light transmitted through the screen or filter. It is desirable to have constructions which provide increased light throughput.
Generally, rear projection screens have suffered from poor angularity. Angularity is the term used to describe the ability of a viewer to see a good image from the screen or filter at some angles other than those which are ordinary to the screen surface. As the viewer moves to the side of the screen or filter, the image quality is decreased. It is desirable to have screens and filters which have improved angularity.
U.S. Pat. Nos. 5,563,738 and 5,781,344, (Vance), relate to light transmitting and dispersing filters having low reflectance. The multi-layer light filters use the addition of optical layers to a basic refractive light filter to allow adjustment of gain, contrast and ambient light rejection of light filters.
U.S. Pat. No. 6,076,933 (DiLoreto et al) describes light transmitting and dispersing filters similar to those described by Vance with the addition of a conformal layer of light transmissive material on the back surface of the transparent beads.
Rear projection screens typically contain mechanisms such as minute colloidal particles to diffuse the light into the desired viewing space. When these screens are used with high magnification systems in which the projection beam is nearly coherent, an undesirable artifact in the form of a speckle pattern (e.g., bright pin holes) often is observed. The speckle pattern is most pronounced in screens with high gains. Speckle reduction has been discussed in the literature. It is known for example that to reduce the visibility of speckle, the coherence of the illumination beam must be destroyed. One method which has been suggested is to move one diffusion screen with respect to another and separating the diffusing surfaces. When modifying the screens to reduce speckle, however, it is important not to deteriorate the resolution on the screen.
This invention relates to light transmitting filters comprising:
(a) a light absorbing layer of material having a front surface and a back surface,
(b) transparent microspheres embedded in the light absorbing layer and contacting the front surface of the light absorbing layer with portions of the microspheres protruding through the back surface of the light absorbing layer for transmitting light through the light absorbing layer, and
(c) a conformed layer of optically clear material having a front surface and a back surface wherein the front surface of the conformed layer is in contact with and conforming in shape with the protruding portions of the microspheres, and wherein the back surface of the conformed layer has a textured finish.
The invention also relates to methods of making these light transmitting filters. The light transmitting filters of the present invention have improved light throughput and improved angularity. The use of the light filters of the invention in rear projection screens substantially reduces speckle without materially affecting the percentage of light transmitted through the screen.